1. Field of Inventions
The present inventions relate generally to devices for performing diagnostic and therapeutic operations on body tissue.
2. Description of the Related Art
There are many instances where diagnostic and therapeutic elements must be positioned adjacent to body tissue. One instance involves the formation of therapeutic lesions to the treat cardiac conditions such as atrial fibrillation, atrial flutter and arrhythmia. Therapeutic lesions may also be used to treat conditions in other regions of the body including, but not limited to, the prostate, liver, brain, gall bladder, uterus and other solid organs. Typically, the lesions are formed by ablating tissue with one or more electrodes. Electromagnetic radio frequency (“RF”) energy applied by the electrode heats, and eventually kills (i.e. “ablates”), the tissue to form a lesion. During the ablation of soft tissue (i.e. tissue other than blood, bone and connective tissue), tissue coagulation occurs and it is the coagulation that kills the tissue. Thus, references to the ablation of soft tissue are necessarily references to soft tissue coagulation. “Tissue coagulation” is the process of cross-linking proteins in tissue to cause the tissue to jell. In soft tissue, it is the fluid within the tissue cell membranes that jells to kill the cells, thereby killing the tissue. Depending on the procedure, a variety of different electrophysiology devices may be used to position a plurality of electrodes at the target location.
In recent years, devices such as surgical soft tissue coagulation probes (or “probes”) that carry one or more diagnostic or therapeutic elements have been developed. These probes may be used, for example, in endocardial and epicardial procedures where access to the heart is obtained by way of a thoracostomy, thoracotomy or median stemotomy. Such probes also allow endocardial lesions to be formed as a secondary procedure during a primary open heart surgical procedure such as mitral valve replacement, aortic valve replacement, and coronary artery bypass grafting. In either case, it is frequently desirable to create continuous transmural linear lesions for therapeutic purposes.
One method of increasing the effectiveness of surgical probes involves the injection of conductive fluid into the target tissue before and/or during the tissue coagulation procedure. U.S. Pat. No. 6,814,731 discloses surgical probes that include jet injectors which inject conductive fluid into tissue as well as electrodes that transmit energy to tissue. The conductive fluid decreases the electrical resistance of the tissue in the vicinity of the electrodes. The decrease in electrical resistance shifts the hottest isothermal region deeper into the tissue, thereby enabling higher power to be delivered without causing char or excessive surface desiccation to occur. Higher power results in a larger volume of tissue being heated to a temperature sufficient to coagulate tissue (above 50° C.) and, therefore, a wider and deeper lesion. Lesion depth is important because lesions which are not transmural may fail to cure the patient's medical condition.
The present inventor has determined that devices which inject fluid into tissue are susceptible to improvement. For example, the present inventor has determined that there are instances where the orientation of the jet injectors relative to the target tissue is important and that it would be desirable to insure that the proper orientation of the jet injectors, as well as good jet injectors/tissue contact, is established and maintained.